A TPMS (Tire Pressure Monitoring System), which monitors the air pressure in each of tires mounted on a vehicle, is known. In a conventional TPMS, a sensor unit that detects air pressure is attached to each tire, and detection results are transmitted wirelessly to a monitoring apparatus provided in the vehicle body. It is necessary for the monitoring apparatus to distinguish the tire to which the received detection results pertain.
JP 2012-224230A discloses a tire position determination system including tire valves provided in each of tires in a vehicle, and a wireless signal transmitter provided in a position that is a different distance from each of the tires. Each tire valve receives the wireless signal transmitted by the transmitter, and it is determined which tire valve the wireless signal is from on the basis of a reception strength of the wireless signal at each tire valve.
JP 2013-123997A discloses a wheel position determination apparatus in which an RF signal transmission circuit is provided in a tire sensor unit in each of tires, and an antenna of a receiver unit that receives the RF signals is disposed in a position a different distance from each of the transmission circuits. The apparatus determines the position of the tire sensor units on the basis of reception strengths of the RF signals from the tire sensor units at the receiver unit.
According to the tire position determination system disclosed in JP 2012-224230A, it is necessary for the wireless signal transmitter to be provided in a different position from each of the tires. There is thus a problem in that the position where the transmitter can be installed in the vehicle is limited. Likewise, according to the wheel position determination apparatus disclosed in JP 2013-123997A, it is necessary for the antenna of the receiver unit to be disposed in a position that is a different distance from each of the transmission circuits in the tire sensor units, and there is thus a problem in that the position where the antenna can be installed is limited. There is a risk that such limitations on the position where such vehicle-side communication devices, such as transmitters and receiver units, can be installed in a narrow space such as a vehicle will greatly interfere with the overall design of the vehicle. Also, because the signal strength of an RF signal undergoes little attenuation with respect to distance, it is not easy to accurately determine the positions of four wheels that are at only slightly different distances.
Having been achieved in light of such circumstances, it is an object of the present invention to provide a communication device mounting position determination system and a determination apparatus capable of relaxing limitations on where a vehicle-side communication apparatus can be installed in a vehicle, and capable of accurately determining the mounting position of a communication device.